The field of the invention relates generally to electronic trip units (ETUs) and more particularly to power management within an ETU.
An electronic trip unit is a device which protects a circuit and equipment connected to the circuit. In industrial settings, for example, an ETU serves to prevent damage to equipment and machines that, in many cases, represent a significant investment by a business and on whose operation the business relies. An ETU carries out this function by monitoring electrical current across a line and, if the current exceeds a certain threshold, will open a switch in the line, thereby preventing further current from reaching devices that would be damaged by the excessive current. The switch may be opened and closed by, for example, an electromechanical actuator.
Given the role that an ETU plays in protecting the equipment connected to it, it is beneficial to determine whether the ETU is in proper working order, through diagnostics and maintenance. Generally, at least one piece of electrical equipment external to the ETU is utilized to determine the status of an ETU, including whether any malfunctions have occurred. Usually, such a piece of equipment is carried by a technician (“user”) and requires an external source of power, which the user must locate and draw power from, in order to proceed with servicing an ETU. In many instances external power sources are not readily available. Simply including a power bus port for a peripheral device in an ETU would put the ETU at risk of losing its primary functionality of protecting a circuit. That is, ETUs are typically self-powered devices that do not have a predictable input power, which is typically proportional to circuit breaker load current. Accordingly, an ETU may not be able to supply output power to a peripheral device during low input power conditions without collapsing ETU busses and compromising standard ETU protections.